In moving picture processing, it is required to handle interframe motions due to such conditions as movements of objects in respective frames or camera panning operations. Although the contents of the current frame are different from those of the previous frame, there is a high degree of correlation therebetween. Motion compensation is a technique of analyzing pictures for interframe prediction, wherein successive frames are compared to provide motion vector data representing the direction and extent of movement of each object. Through motion compensation, picture data can be reduced in size at a substantially high rate of compression. In most schemes of picture frame coding, it is common practice to partition each picture frame into predetermined blocks of pixels. The use of smaller-sized blocks makes it possible to carry out motion-compensated prediction in further detail. On the other hand, however, due to an increase in the number of blocks, motion vector data tends to increase to cause an increase in the amount of coding, which results in a requirement for higher processing power in hardware. Further, if no filter processing is performed in picture data encoding at a low bit rate, block artifacts are incurred at the step of decoding, and picture data containing the block artifacts is stored into frame memory. Then, at the time of decoding the next frame data through reference to the picture data containing the artifacts, there occurs a propagating condition of picture quality degradation. Hence, for preventing the occurrence of such propagation of picture quality degradation, it is required to carry out filter processing.
In conventional filter processing on picture data, a predetermined number of taps is adopted. Thus, since a filter coefficient value per frame is constant, the same filter processing is performed at any picture position as described in Non-patent Document 1 indicated below.
Further, there is known a technique for performing filter processing on picture data by means of microprogramming (as disclosed in Patent Document 1 indicated below, for example). In this technique, according to a microprogram, picture data is read out of memory and relevant clock data is input to a picture processing section for execution of picture data filtering.
Patent Document 1:
Japanese Unexamined Patent Publication No. 2002-8025
Non-patent Document 1:
ITU-T H.264 (03/2005), “Advanced video coding for generic audio visual services”